December 28, 2011: The U.S. Department of Defense has halted work on its U.S. Air Force ALT (Airborne Laser Testbed). The project will be put into storage until such time as more effective technology is available to revive the effort, or it is decided that the ALT is not worth the storage expense. ATL has cost over $5 billion during the last 16 years. It never worked, at least not in a practical sense. A year ago, for the second time in a row, the ALT failed in an attempt to use its laser to destroy a ballistic missile. That time, the problem was with the radar and fire control system, which failed to lock the laser on the actual missile (although the radar did detect the actual missile launch). In the past the main problem has been a lack of power to drive the laser to lethal levels. Because of that the ALT program has been an expensive near miss for nearly two decades. Two years ago ALT was demoted from a system in development to a research program. The reason for this was all about energy supply. Even if ALT worked flawlessly, it does not have enough energy to hit a launching missile from a safe (from enemy fire) distance. ALT needs more than twenty times as much energy than it has now and it will be a while before that problem is solved.
There have been some successes with this kind of weapon. Last year, the U.S. Navy successfully tested their laser weapon, using it to destroy a UAV. This was the seventh time the navy laser has destroyed a UAV this way. The laser cannon was mounted on a KINETO Tracking Mount, which is similar, but larger (and more accurate than) the mount used by the Phalanx CIWS (Close In Weapons System). The navy laser weapon test used the radar and tracking system of the CIWS. Last year, CIWS was upgraded so that its sensors could detect speedboats, small aircraft, and naval mines. The problem here is that knocking down UAVs is not something that the navy needs help with and the current laser gun technology has to be improved quite a bit before it's worth mounting on a ship.
Six years ago, manufacturers of combat lasers believed these weapons were only a few years away from battlefield use. To that end, Northrop-Grumman set up a new division to develop and build battle lasers. This optimism was caused by two successful tests seven years ago. In one, a solid state laser shot down a mortar round. In another, a much more powerful chemical laser, hit a missile type target. Neither of these tests led to any useable weapons and the combat laser remains the "weapon of the future". The basic problems are reliability and ammo (power to generate the laser).
Solid state lasers have been around since the 1950s and chemical lasers first appeared in the 1970s. The chemical laser has the advantage of using a chemical reaction to create the megawatt level of energy for a laser that can penetrate the body of a ballistic missile that is still rising in the air hundreds of kilometers away. The chemical reaction uses atomized liquid hydrogen peroxide and potassium hydroxide and chlorine gas to form an ionized form of oxygen known as singlet delta oxygen (SDO). This, in turn is rapidly mixed with molecular iodine gas to form ionized iodine gas. At that point, the ionized iodine gas rapidly returns to its resting state, and while doing so releases photons pulsing at the right frequency to create the laser light. These photons are channeled by mirrors and sent on their way to the target (which is being tracked and pinpointed by other lasers). The airborne laser weighs about six tons. It can be carried in a C-130H, producing a laser powerful enough to hit airborne or ground targets fifteen kilometers away. The laser exits via a targeting turret under the nose of the aircraft. The laser beam is invisible to the human eye. The chemicals are mixed at high speeds and the byproducts are harmless heat, potassium salt, water, and oxygen. A similar laser, flying in a larger aircraft (B-747 based ALT) was supposed to have enough range to knock down ballistic missiles as they took off. But the ALT never developed sufficient range to be an effective weapon.
Nearly half a century of engineering work has produced thousands of improvements, and a few breakthroughs, in making the lasers more powerful, accurate, and lethal. More efficient energy storage has made it possible to use lighter, shorter range ground based lasers effective against smaller targets like mortar shells and short-range rockets. Northrop's move was an indication that the company felt confident enough to gamble its own money, instead of what they get for government research contracts, to produce useful laser weapons. A larger high energy airborne laser would not only be useful against ballistic missiles but enemy aircraft and space satellites would also be at risk. But companies like Northrop and Boeing are still trying to produce ground and airborne lasers that can successfully operate under combat conditions. The big problem with anti-missile airborne lasers has always been the power supply. Lots of chemicals are needed to generate sufficient power for a laser that can reach out for hundreds of kilometers and do sufficient damage to a ballistic missile. To be effective the airborne laser needs sufficient power to get off several shots. So far, no one has been able to produce such a weapon. That's why these lasers remain "the weapon of the future" and will probably remain so for a while.